1. Field of the Invention
The present invention relates to a solid state imaging device capable of automatic focusing of a phase difference method or stereoscopy.
2. Description Related to the Prior Art
A solid state imaging device having a plurality of photodiodes (PDs) which selectively receive light depending on an incident angle and capable of automatic focusing of a phase difference method (hereinafter referred to as the phase difference AF) is known (see Japanese Patent Laid-Open Publication No. 59-033409, U.S. Pat. No. 6,829,008 corresponding to Japanese Patent Laid-Open Publication No. 2000-156823, and Japanese Patent Laid-Open Publication No. 2007-158109).
The solid state imaging device, disclosed in the Japanese Patent Laid-Open Publication No. 59-033409 and the U.S. Pat. No. 6,829,008, has pixels (hereinafter referred to as the phase difference detection pixels) that selectively receive light depending on the incident angle. In each phase difference detection pixel, the optical axis of a microlens that condenses light onto the PD is not coincident with the center of an opening formed through a light shielding film that covers the PD. In this case, an area of the opening needs to be reduced by the amount of eccentricity or shift of the opening of the light shielding film. This makes the sensitivity of the phase difference detection pixel lower than that of the normal pixel with the optical axis of the microlens coincident with the center of the opening of the light shielding film.
The solid state imaging device suggested in the Japanese Patent Laid-Open Publication No. 2007-158109 is provided with a pupil forming microlens that covers two phase difference detection pixels. Two pupil-splitting microlenses corresponding to the respective phase difference detection pixels are provided below the pupil forming microlens that separates light beams. Thereby, the PD of each phase difference detection pixel selectively receives the light beams depending on the incident angle. When the light beams are separated by the pupil forming microlens, and the separated light beams are condensed by the pupil splitting microlenses and incident on the PDs of the phase difference detection pixels, respectively, it is not necessary to reduce the size of the opening of the light shielding film. Thereby, the size of the opening is made the same as that of the normal pixel. This improves the sensitivity of the phase difference detection pixel compared with that of a conventional phase difference detection pixel.
The configuration disclosed in the Japanese Patent Laid-Open Publication No. 2007-158109 improves the sensitivity of the phase difference detection pixels. However, a process for forming the pupil forming microlens is additionally needed, and the thickness of the microlens is increased. Thereby, material for the microlens is increased and the processing of the microlens becomes difficult. As a result, cost for the solid state imaging device increases. In addition to the configuration described above, a configuration in which the optical axis of the microlens is shifted from the center of the light receiving surface of the PD is known. In this configuration, the diameter of the microlens needs to be reduced by the amount of eccentricity or shift. This reduces the sensitivity of the phase difference detection pixels similar to the case with the eccentric or shifted openings of the light shielding film. Thus, it is desired to improve the sensitivity of the phase difference detection pixels in the solid state imaging device employing the phase difference AF with no cost increase.